The present invention relates to a control device used in an image forming apparatus whose main body is connected to one or more options through two-way serial lines comprising transmission and reception lines and capable of determining the state of each of the options.
Description is made using an electrophotographic copying apparatus which is one example of an image forming apparatus. Recent electrophotographic copying apparatuses have a lot of functions and can be provided with various options. For example, an electrophotographic copying apparatus can be provided, as an option, with a soter for sorting copied sheets, an automatic document feeder (referred to as ADF hereinafter) for automatically setting a document, a special cassette in which a great many paper sheets can be contained, a duplex copy unit for making duplex copies, various display devices, or the like. In addition, some options may be, in some cases, provided for the main body of the electrophotographic copying apparatus as standard equipment.
When the main body of the electrophotographic copying apparatus is provided with the above option, the main body and the option are connected through a connecting line such that signals can be transmitted and received. A system using a serial line comprising a feeding line and a receiving line as an example of this connecting line has been proposed. In this proposed system, a signal is applied to the option from a main body controller in the electrophotographic copying apparatus through the feeding line and correspondingly, a response signal is sent back to the main body controller from the option through the receiving line.
In the system comprising such a serial line, when there occurs an abnormality in any one of a plurality of the options connected to the main body of the electrophotographic copying apparatus, for example, an abnormality in the connection betweem the main body and the option or an abnormality in the option itself, the abnormality must be quickly detected. An apparatus for quickly detecting an abnormality in an option has been proposed in Japanese Patent Laid-Open Gazette No. 103297/1986. More specifically, proposed is an apparatus, adapted such that a response signal is sent back from each option with respect to data sent out from a main body controller in an electrophotographic copying apparatus, for determining that an error occurs in the option when the response signal is not sent back a predetermined number of times with respect to the data repeatedly sent out from the main body controller in the electrophotographic copying apparatus. Consequently, it can be immediately determined which option is erroneous.
Meanwhile, when an abnormality is detected in an option, a case is rare where the option itself is not operated by a failure. In many cases, an abnormality is caused by elementary errors, for example, such errors that the main body of the electrophotographic copying apparatus and the option are not connected or the power supply of the option is off. When such an abnormality is detected, it is preferable to determine whether the main body of the electrophotographic copying apparatus and the option are not connected or not, or the power supply of the option is off or not and automatically perform predetermined processing on the basis of the results of the determination.
However, in the above described apparatus proposed in Japanese Patent Laid-Open Gazette No. 103297/1986, it can not be determined whether the main body of the electrophotographic copying apparatus and the option are not connected or not, or the power supply of the option is off or not. Accordingly, even if the abnormality in the option is detected, processing conforming to the contents of the abnormality can not be automatically performed.
Although description was made using an electrophotographic copying apparatus as an example, a printer which can be equipped with a sorter and a special cassette has been commercially available in recent years. In such a printer, there is the same problem to be solved.